Synchronizing method and apparatus using error detection of sequence numbers to avoid synchronizing failure

ABSTRACT

The present invention relates to transmissions and retransmissions of packet data, particularly ciphered data, in a communications system. Especially, it relates to radio link transmissions and avoidance of deciphering failures in a cellular mobile radio system, particularly a Universal Mobile Telecommunications System, UMTS, or WCDMA system.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to transmissions and retransmissions ofpacket data in a communications system. Especially, it relates to radiolink transmissions and avoidance of deciphering failures in a cellularmobile radio system, particularly a Universal Mobile TelecommunicationsSystem, UMTS, or WCDMA system.

BACKGROUND AND DESCRIPTION OF RELATED ART

In many radio communications system, such as UMTS, ciphering orencryption protects user data and signaling confidentiality. Fordetection of transmission errors data is also protected by an errordetecting code. For this purpose a cyclic redundancy check code orCRC-code is used.

Within this patent application, a radio network controller, RNC, isunderstood as a network element including an RRM (Radio ResourceManagement) entity. The RNC is connected to a fixed network. Node B is alogical node responsible for radio transmission/reception in one or morecells to/from a User Equipment. A base station, BS, is a physical entityrepresenting Node B.

With reference to FIG. 1, base stations <<BS 1>> and <<BS 2>> arephysical entities representing Nodes B <<Node B 1>> and <<Node B 2>>respectively. <<Node B 1>> and <<Node B 2>> terminate the air interface,called Uu interface within UMTS, between UE and respective Node Btowards the radio network controller <<RNC>>. <<RNC>> is connected to afixed network <<Network>>.

In FIG. 1, the base stations are connected to the same radio networkcontroller RNC. However, this specification also covers the exemplarysituation where the base stations are connected to different RNCs. InUMTS, the RLC protocol is terminated in a serving RNC, SRNC, responsiblefor interconnecting the radio access network of UMTS to a core network.

3^(rd) Generation Partnership Project (3GPP): Technical SpecificationGroup Radio Access Network, Radio Interface Protocol Architecture, 3GPPTS 25.301 v3.6.0, France, September 2000, describes an overall protocolstructure of a Universal Mobile Telecommunications System (UMTS). Thereare three protocol layers:

-   -   physical layer, layer 1 or L1,    -   data link layer, layer 2 or L2, and    -   network layer, layer 3 or L3.

Layer 2, L2, and layer 3, L3 are divided into Control and User Planes.Layer 2 consists of two sub-layers, RLC and MAC, for the Control Planeand four sub-layers, BMC, PDCP, RLC and MAC, for the User Plane. Theacronyms BMC, PDCP, RLC and MAC denote Broadcast/Multicast Control,Packet Data Convergence Protocol, Radio Link Control and Medium AccessControl respectively.

FIG. 2 displays a simplified UMTS layers 1 and 2 protocol structure fora Uu Stratum, UuS, or Radio Stratum, between a user equipment UE and aUniversal Terrestrial Radio Access Network, UTRAN.

Radio Access Bearers, RABs, are associated with the application fortransportation of services between core network, CN, and user equipment,UE, through a radio access network. Each RAB is associated with qualityattributes such as service class, guaranteed bit rate, transfer delay,residual BER, and traffic handling priority. An RAB may be assigned oneor more Radio Bearers, RBs, being responsible for the transportationbetween UTRAN and UE. For each mobile station there may be one orseveral RBs representing a radio link comprising one or more channelsbetween UE and UTRAN. Data flows (in the form of segments) of the RBsare passed to respective Radio Link Control, RLC, entities which amongstother tasks buffer the received data segments. There is one RLC entityfor each RB. In the RLC layer, RBs are mapped onto respective logicalchannels. A Medium Access Control, MAC, entity receives data transmittedin the logical channels and further maps logical channels onto a set oftransport channels. In accordance with subsection 5.3.1.2 of the 3GPPtechnical specification MAC should support service multiplexing e.g. forRLC services to be mapped on the same transport channel. In this caseidentification of multiplexing is contained in the MAC protocol controlinformation.

Transport channels are finally mapped to a single physical channel whichhas a total bandwidth allocated to it by the network. In frequencydivision duplex mode, a physical channel is defined by code, frequencyand, in the uplink, relative phase (I/Q). In time division duplex mode aphysical channel is defined by code, frequency, and timeslot. As furtherdescribed in subsection 5.2.2 of the 3GPP technical specification the L1layer is responsible for error detection on transport channels andindication to higher layer, FEC encoding/decoding andinterleaving/deinterleaving of transport channels.

Segmentation and reassembly of data units are performed betweendifferent protocol layers as schematically illustrated in FIG. 3.

A MAC protocol data unit, MAC PDU, also called transport block, TB, isthe basic unit passed down to L1 from MAC layer.

A number of MAC PDUs shown in FIG. 3 shall comprise a transport blockset. Note, however, that in all cases a transport block set need notnecessarily match with an RLC SDU. The span of a transport block set canbe smaller or larger than an RLC SDU.

Transport blocks, TBs, passed to L1 from MAC at the same time instanceand using the same transport channel form a transport block set.

A higher layer PDU can be reassembled by simply concatenating all RLCPDUs included in a transport block set as implied by the used transportformat.

A transmission time interval, TTI, is defined as the interarrival timeof Transport Block Sets, i.e. the time it should take to transmit atransport block set.

A transport format is defined as a format offered by L1 to MAC for thedelivery of a Transport Block Set during a Transmission Time Interval ona Transport Channel, and is a combination of encodings, interleaving,bit rate and mapping onto physical channels.

3^(rd) Generation Partnership Project (3GPP): Technical SpecificationGroup Radio Access Network, Multiplexing and channel coding (FDD), 3GPPTS 25.212 v4.4.0, France, March 2002, describes different generatorpolynomials of CRC-codes used in UMTS. The respective generatorpolynomials areg ₂₄(x)=1+x+x ⁵ +x ⁶ +x ²³ +x ²⁴,g ₁₆(x)=1+x ⁵ +x ¹² +x ¹⁶,g ₁₂(x)=1+x+x ² +x ³ +x ¹¹ +x ¹²,g ₈(x)=1+x+x ³ +x ⁴ +x ⁷ +x ⁸.

The respective number of parity bits in the resulting code word equalsthe exponent of the highest power term of the respective generatorpolynomial. Which CRC-code to use for each Transport Channel, TrCH, issignaled from protocol layers above L2/MAC layer.

3^(rd) Generation Partnership Project (3GPP): Technical SpecificationGroup Radio Access Network, Radio Link Control (RLC) protocolspecification, 3GPP TS 25.322 v4.4.0, France, March 2002, specifies theRLC protocol. The RLC layer provides three services to the higherlayers:

-   -   transparent data transfer service,    -   unacknowledged data transfer service, and    -   acknowledged data transfer service,        in the sequel referred to as transparent mode, TM,        unacknowledged mode, UM, and acknowledged mode, AM,        respectively.

The 3GPP specification describes in chapter 9 elements for peer-to-peercommunication. No RLC overhead is added for transparent mode dataprotocol data units, TMD-PDUs. Unacknowledged mode data protocol dataunits, UMD-PDUs, and acknowledged mode protocol data units, AMD-PDUs,are sequentially numbered. The sequence number, SN, parameter comprises12 bits for AMD-PDUs and 7 bits for UMD-PDUs. SN is a modulo-integersequence number, where the integer equals 4096 and 128 for AM and UMrespectively. A hyper frame number indicator, HFNI, indicates a hyperframe number, HFN, to the peer entity. With the aid of this field HFN ofUE and UTRAN, respectively, can be synchronized. Section 9.7.3 of the3GPP specification describes SDU discard function for acknowledged,unacknowledged, and transparent modes.

3rd Generation Partnership Project (3GPP): Technical Specification GroupServices and System Aspects, 3G Security, Security Architecture, 3GPP TS33.102 v4.3.0, France, December 2001, shows 3G security architecture.Four security features are provided with respect to confidentiality ofdata on a network access link:

-   -   cipher algorithm agreement,    -   cipher key agreement,    -   confidentiality of user data, and    -   confidentiality of signaling data.

Section 6.4.8 of the 3GPP technical specification describesinitialization of synchronization for ciphering and integrityprotection. HFN and SN are initialized. HFN and SN form a COUNT-Cvariable, the 32-bit values of which are input to the cipheringalgorithm. Section 6.6.4.1 of the 3GPP technical specification revealsthe composition of COUNT-C in UMTS. HFN is incremented each SN cycle.

International Patent Application WO0156249 reveals synchronization ofencrypted data by means of sequence numbers. The sequence numbers areunencrypted and unencoded. Missing sequence numbers are used to detectlost data packets. A requirement of stream encryption algorithms is thatthe transmitting side and the receiving side be synchronized.

None of the cited documents above discloses a method and system forexploring the inherent redundancy of the unencoded sequence numbers SNs,for avoidance of cipher synchronization failure and whereby theredundancy of CRC-encoded data can be reduced. Particularly, none of thecited documents reveals a method and system of disregarding erroneoussequence numbers or a method and system of HFN update, reducing the riskof erroneous HFN update due to SN containing one or more transmissionerrors or lost SNs.

SUMMARY OF THE INVENTION

HFN is normally not transmitted over air, with initialization being oneimportant exception. HFN is updated in both transmitter and receivereach time SN recycles.

When SN is subject to transmission errors or when a data packet carryingan SN is lost there is risk of erroneous updating of HFN. Prior artreveals solution for acknowledged mode making use or error detection ofencoded data for ordering retransmission. However, for unacknowledgedmode this option is not available. Further, for many applications,particularly real-time applications it is desirable to uselow-redundancy error detecting codes or, in some cases, no errordetecting code.

Consequently, it is an object of this invention to provide a method andsystem keeping synchronism in case of lost or erroneous SNs withoutrelying on a CRC error detecting code.

It is also an object to detect lost or erroneous sequence numbers, SNs.

A further object is to leave HFN unaffected by lost or erroneous SNs.

Finally, it is an object to introduce a mechanism for eliminating theeffect of occasional erroneous or lacking SNs.

These objects are met by the invention, which is particularly wellsuited for a Universal Mobile Telecommunications System, UMTS,disregarding SNs considered invalid when determining HFNs.

Preferred embodiments of the invention, by way of examples, aredescribed with reference to the accompanying drawings below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows communication between a UE and a base station involved in aconnection between an RNC and the UE.

FIG. 2 displays a layered protocol structure, according to prior art, ina radio communications system.

FIG. 3 schematically illustrates segmentation and reassembly of dataunits for different protocol layers.

FIG. 4 illustrates a basic method of updating HFN at receiver side uponreceipt of PDUs.

FIG. 5 shows a block diagram illustrating a first embodiment of theinvention comparing a prediction estimate and received sequence number.

FIG. 6 shows a flow chart illustrating a first embodiment of theinvention.

FIG. 7 illustrates a second embodiment of the invention, consideringPDUs within a sliding decision-window.

FIG. 8 shows three cases with exemplary sequences illustrating thesecond embodiment.

DESCRIPTION OF PREFERRED EMBODIMENTS

With reference to FIG. 1, encrypted or ciphered data is transmitted overthe radio interface between <<UE/Client Device>> and <<BS 2/Node B 2>>.In uplink direction <<BS 2/Node B 2>> represents the receiver side ofthe radio interface and in downlink direction receiver side isrepresented by <<UE/Client Device>> and <<BS 2/Node B 2>> is on thetransmitter side. Encrypted or ciphered data is transmitted from thetransmitter side to the receiver side in protocol data units, PDUS.

On the transmitter side it is a trivial matter to increase HFN as asequence number counter starts a new cycle. However, this is not thecase on the receiver side. First, the receiver side should use the sameHFN as the transmitter side. Second, during PDU transmissions some PDUsmay be lost. The receiver side should nevertheless use correct HFN andupdate HFN correctly in order not to loose synchronism.

FIG. 4 shows a basic method of updating HFN at receiver side uponreceipt of PDUs, each PDU including a sequence number, SN. According tothe method a new cycle of sequence numbers is assumed to be started whenthe most recently received sequence number, SN_(i), is less than thesequence number, SN_(i-1), of the PDU received consecutively precedingthe most recently received PDU. Not restricting HFN to increase only atsequence number 0, the basic method updates HFN correctly also if one ormore PDUs are lost during transmission.

A basic method, e.g. as described above in relation to FIG. 4, does notnecessarily increase HFN correctly in case of transmission errors. Sincetransmitter side increases HFN irrespective of whether it is increasedat receiving side, this could result in lost synchronism betweentransmitting and receiving sides.

FIG. 5 shows a block diagram and FIG. 6 shows a flow chart illustratinga first embodiment of the invention where sequence numbers are purgedfrom a, real or fictitious, list according to the conditionSN _(n) >SN _(n-1)+Δ_(max)(mod I), where  (1)Δ_(max) =N _(TTI) ·TB _(max)+δ,  (2)prior to determining HFN with a basic method, such as the methoddescribed in relation to FIG. 4, at the receiver side. In equation (1)I=4096 for acknowledged mode and I=128 for unacknowledged mode whenapplied to UMTS according to cited 3GPP specification. SN_(n) is thesequence number with list index n and SN_(n-1) is the sequence number ofthe PDU received immediately preceding a remaining PDU with sequencenumber SN_(n). In FIG. 6, the modulus operation of equation (1) has notbeen indicated for reasons of readability. Calculation modulo I inequation (1) relies on the cyclic characteristic of the sequencenumbers. When the cycle length of the sequence numbers changes, so doesI. In equation (2), N_(TTI) is the number of transmission timeintervals, TTIs, when no data is received and TB_(max) is the maximumnumber of transport blocks in the transport format, TF, of thecorresponding transport channel. After proper disregarding of one ormore erroneous sequence numbers, in FIG. 6 illustrated by purging thesequence number from a list arranged according to arrival time, theremaining sequence numbers are used as input for basic updating of HFN.

Disregarding an SN as regards deciphering synchronization does not implythat the corresponding PDU necessarily is discarded from RLC. Nor doesit imply that the PDU is not discarded. Preferably, according to theinvention corresponding PDU is not discarded from RLC.

By adding a term, δ=2, in equation (2) one RLC discard operation or RLCreconfiguration is allowed between two consecutively received PDUs. Foreach disregarded SN, δ is increased by 1. When an SN is not disregarded,δ is reset to 2.

The first embodiment of the invention can, alternatively, be consideredas a prediction of the next received sequence number, considering lostPDUs. In FIG. 5 sequence numbers <<SNs>> as received are input to aprediction entity <<Prediction>> and an optional storage element<<Buffer>> allowing for time alignment of received data with predicteddata as need be. The greater the number of lost PDUS, estimated from thenumber of transmission time intervals with no received PDUs and themaximum number of transport blocks in the transport format, the greaterthe prediction interval of sequence numbers to come. If the nextsequence number is not within the prediction interval it is disregarded.In FIG. 5 this is performed in entity <<Cmp & Purge>>. The purgedsequence of sequence numbers <<Purged SNs>> is then fed to basic HFNupdate, e.g. an entity operating according to the updating described inrelation to FIG. 4.

If, e.g., a transmitted sequence of sequence numbers is . . . 5, 6, 7,8, 9, 10, 11, . . . and the received sequence is . . . 5, 6, 7, 8, 65,10, 11, . . . and there are no TTIs with no data, then initiallyΔ_(max)=2 according to equation (2). As 6−5=12, 7−6=12 and 8−7=12, nopurging will occur until 65−8=57>2, in the next interval. The sequencenumber transmitted as 9 and received as 65 will be purged, andthereafter treated like a lost sequence number. Consequently Δ_(max) isset to 3, as indicated by equation (2). At receipt of sequence number10, the prediction disregards the received sequence number 65 and thecomparison yields 10−8=23. Consequently sequence number 10 will remainand be transferred for basic HFN updating. At receipt of sequence number11, it is again noted that no TTI is lost since reception of sequencenumber 10, and Δ_(max) is reset to 2. As 11−10=12, sequence number 11will not be disregarded.

If, for the same transmitted sequence as in the preceding paragraph, asmaller sequence number, e.g. 2, were received in place of transmitted9, the comparison would yield, with exemplary modulo 128 calculus(I=128), 2-8=122>2 and the erroneously received sequence numberdisregarded similarly to the case of an erroneously received sequencenumber 65 in the paragraph above.

According to a second embodiment, PDUs within a sliding decision-windowspanning over at least four consecutively received PDUs are considered,when increasing HFN. In an algorithm of increasing HFN not consideringerroneous or lost SNs, such as the algorithm described above, anindicated increase of HFN is disregarded, if the HFN would not beincreased also if any one of the sequence numbers of the slidingdecision-window were disregarded. This is illustrated in the flowchartof FIG. 7. PDUs within a decision window comprising M+1 PDUs areconsidered at decision time-interval of PDU i, i.e. PDUs with sequencenumbers, SNs, in the interval [i−M,i] are considered. One SN or PDU isdisregarded among the M+1 considered PDUs. In FIG. 7, the SN of the mostrecently received PDU is disregarded first. However, any scheme fordisregarding the SNs or PDUs would apply as well, only it guarantees thepossibility of disregarding any one of the SNs of PDUs within thedecision window as need be. If HFN should not be increased according toa basic method of updating HFN, with a sequence number of one PDU beingdisregarded, HFN is left unincreased. The receiver then proceeds withthe next SN/PDU, restarting the flow chart at time interval i+1.However, if HFN would be increased if the SN of the most recentlyreceived PDU were disregarded and not all PDUs' SNs have beendisregarded once, the SN of next PDU within the decision window isdisregarded. This repeats until the SNs of all M+1 PDUs within thedecision window have been disregarded once for the final decision atinterval i or an HFN update according to the basic method does notincrease HFN. If HFN should be increased according to the basic methodof updating when each one of the SNs/PDUs within the decision window isdisregarded, the HFN is updated. Otherwise it is not.

As for the first embodiment, disregarding an SN/PDU as regardsdeciphering synchronization does not imply that the corresponding PDUnecessarily is discarded from RLC in the second embodiment. Nor does itimply that the PDU is not discarded. Preferably, according to theinvention corresponding PDU is not discarded from RLC.

FIG. 8 shows three cases with exemplary sequences illustrating thesecond embodiment. In the first two cases, A and B, an exemplarytransmitted sequence of SNs is . . . 5, 6, 7, 8, 9, 10, . . . in decimalnotion. However, in case A the transmitted SN 9 is erroneously receivedas 2 and in case B it is erroneously received as 65. Assuming that abasic HFN updating at the receiving side increases HFN whenever an SN issmaller than the preceding SN, this would erroneously increase HFN intime interval T1 in case A and in time interval T2 for case B. Thiswould also affect deciphering of a substantial amount of subsequent PDUsdue to lost synchronization. According to the second embodiment of theinvention, this erroneous updating is eliminated at the cost of omitteddecoding of only one PDU by considering all PDUs within the slidingdecision-window. In FIG. 8 a window size equal to 5 is illustrated.

For case A, at time interval T1, the erroneous updating of HFN iscircumvented according to the second embodiment of the invention, sinceif the most recently received PDU with sequence number 2 is disregarded,no updating of HFN would occur in time interval T1. Further, whensliding the decision window one step to the right for making a decisionin time interval T2, again disregarding the sequence number 2 of timeinterval T1, no updating of HFN would occur.

In case B, erroneous updating of HFN in time interval T2 iscircumvented. Again, time interval T1 is within the decision window anddisregarding the sequence number 65 of the PDU received in time intervalT1 would result in HFN not being incremented in time interval T2.

In case C, no transmission error of received PDUs is assumed. HoweverPDUs with sequence numbers 127, 0, 1 and 2 have been lost. Againassuming that HFN is updated when the preceding SN is greater than thecurrent SN, HFN would not be updated in time interval T1, as it wouldaccording to a basic method, such as the one illustrated in FIG. 4, butin time interval T2, since disregarding the sequence number received intime-interval T1 would result in HFN not being increased in accordancewith case A.

If, in the second embodiment of the invention, the window size spannedover less than four PDUs, HFN would not be increased correctly. If,e.g., the window size spanned only three PDUs for the exemplary sequenceof case C in FIG. 8, disregarding sequence number 3 at time interval T1or disregarding sequence number 126 at time interval T2 would leave HFNunchanged, and synchronization would be lost. Preferably the window sizespans over exactly four SNs (PDUs).

Preferably, all system elements, such as UEs and RNCs in UMTS, whereapplicable operate according to the invention. However, the inventioncan also be used in systems also including some equipment, such as UEsand RNCs, not operating according to the invention.

Some exemplary features and characteristics of the invention are listedbelow.

1. A method of failure avoidance when synchronizing a transceiver endand a receiver end by means of transmitted sequence numbers, eachsequence number not necessarily being further error protected, themethod characterized in that a received sequence number considerederroneous according to a predetermined criterion is disregarded.

2. The method according to characteristic 1 characterized in that thecriterion comprises arranging of sequence numbers according to theirtime of arrival and purging of received sequence numbers not beingwithin a prediction interval as determined from earlier received andnon-purged one or more sequence numbers and number of one or moretransmission time intervals with no data received between consecutivelyreceived sequence numbers.

3. The method according to characteristic 2 characterized in that thetransmission time intervals are weighted by the maximum number oftransmission blocks of the transport format.

4. The method according to characteristic 3 characterized in that aninteger is added to the weighted number of transmission intervals.

5. The method according to any of characteristics 2-4 characterized inthat a received sequence number being greater than an estimated greatestsequence number allowed is disregarded.

6. The method according to any of characteristics 2-4 characterized inthat a received sequence number not being greater than an estimatedgreatest sequence number allowed is not disregarded.

7. The method according to any of characteristics 1-6 characterized inthat the purged sequence of sequence numbers is passed to updating of ahyper frame number.

8. The method according to characteristic 7 characterized in that thehyper frame number is updated according to a basic method.

9. The method according to characteristic 1 characterized in that thecriterion comprises arranging of received sequence numbers according totheir time of arrival and for each decision interval sequentiallydisregard each one of the received sequence numbers within a decisionwindow comprising consecutively received sequence numbers.

10. The method according to characteristic 9 characterized in that thedecision window spans over an integer number of consecutively receivedsequence numbers starting with the sequence number of the decisioninterval.

11. The method according to characteristic 9 or 10 characterized in thatthe decision window spans over an integer number of consecutivelyreceived sequence numbers starting with the sequence number of the mostrecently received sequence number.

12. The method according to any of characteristics 9-11 characterized inthat the decision window spans over at least four consecutively receivedsequence numbers.

13. The method according to any of characteristics 9-12 characterized inthat for each disregarded sequence number a candidate hyper frameupdating is undertaken.

14. The method according to characteristic 13 characterized in that thecandidate hyper frame updating is undertaken according to a basicmethod.

15. The method according to characteristic 13 or 14 characterized inthat if, for any one disregarded sequence number within the decisionwindow, the candidate hyper frame number updating results in anon-increased hyper frame number, no further sequence number isdisregarded and no further candidate HFN updating is undertaken for thedecision interval.

16. The method according to any of characteristics 13-15 characterizedin that if, for any one disregarded sequence number within the decisionwindow, the candidate hyper frame number updating results in anon-increased hyper frame number, the hyper frame number of the decisioninterval is set equal to the hyper frame number of the precedingdecision interval.

17. The method according to any of characteristic 13 or 14 characterizedin that if, for all each one of the disregarded sequence numbers withinthe decision window, the candidate hyper frame number updating resultsin the same hyper frame number, this candidate hyper frame number isdecided to be the hyper frame number of the decision interval.

18. The method according to any of characteristic 13 or 14 characterizedin that if, for all each one of the disregarded sequence numbers withinthe decision window, the candidate hyper frame number updating resultsin a hyper frame number increase, the hyper frame number of the decisioninterval is set equal to the hyper frame number of the precedingdecision interval increased by one.

19. The method according to characteristics 8 or 14 characterized inthat the basic method increases a hyper frame number if, when comparingtwo received sequence numbers, the most recent of the two sequencenumbers is less than the other sequence number.

20. The method according to characteristic 19 characterized in that thecomparison is made modulo an integer, the integer being equal to thecycle length of transmitted sequence numbers.

21. The method according to any of characteristics 1-20 characterized inthat it is a method of avoiding cipher synchronization failure.

22. The method according to any of characteristics 1-21 characterized inthat it allows for reduction of redundancy being added to payload.

23. An element for receiving one or more transmitted sequence numberssynchronizing to a transceiver end by means of the transmitted sequencenumbers, each sequence number not necessarily being further errorprotected, the element characterized by processing means fordisregarding one or more sequence numbers considered erroneous.

24. The element according to characteristic 23 characterized in that thedisregarding of one or more sequence numbers reduces or eliminates therisk of synchronization failure.

25. The element according to characteristic 23 or 24 characterized inthat the processing means disregards sequence numbers in accordance withthe method in any of characteristics 1-22.

26. An element for receiving one or more transmitted sequence numberseach sequence number not necessarily being further error protected, theelement characterized by prediction means for prediction of a mostrecent sequence number from one or more earlier sequence numbers andcomparison means for comparing the predicted sequence number with areceived counterpart and for conditionally disregarding the receivedsequence number being the prediction counterpart.

27. The element according to characteristic 26 characterized by thecomparison means conditionally disregarding the received sequence numberbeing the prediction counterpart if it exceeds a threshold value.

28. The element according to characteristic 27 characterized in that thethreshold value is determined including as a parameter number oftransmission time intervals with no received data since consecutivelyformerly received sequence number was received.

29. The element according to characteristic 28 characterized in that thenumber of transmission time intervals are weighted with a factor equalto the maximum number of transmission blocks of a current transportformat.

30. The element according to characteristic 29 characterized by thecomparison means comprising transfer means for transferring thenon-disregarded sequence numbers to an entity of basic hyper framenumber updating.

31. The element according to characteristic 30 characterized by theentity of basic hyper frame number updating updates one or more hyperframe numbers according to the method in characteristic 19 or 20.

32. The element according to any of characteristics 23-31 characterizedin that the element is included in or is a radio network controller.

33. The element according to any of characteristics 23-31 characterizedin that the element is included in or is a user equipment.

34. The element according to any of characteristics 23-33 characterizedin that the element is an element of UMTS or a WCDMA system.

35. A radio communications system characterized by means for carryingout the method in any of characteristics 1-22.

36. A radio communications system characterized by one or more elementsaccording to any of characteristics 23-34.

A person skilled in the art readily understands that the receiver andtransmitter properties of a BS or a UE are general in nature. The use ofconcepts such as BS, UE or RNC within this patent application is notintended to limit the invention only to devices associated with theseacronyms. It concerns all devices operating correspondingly, or beingobvious to adapt thereto by a person skilled in the art, in relation tothe invention. As an explicit non-exclusive example the inventionrelates to mobile stations without a subscriber identity module, SIM, aswell as user equipment including one or more SIMs. Further, protocolsand layers are referred to in close relation with UMTS and Internetterminology. However, this does not exclude applicability of theinvention in other systems with other protocols and layers of similarfunctionality. As a non-exclusive example, the invention applies forradio resource management interfacing of a connection protocolapplication layer as well as interfacing of a connection protocoltransport layer, such as TCP.

The invention is not intended to be limited only to the embodimentsdescribed in detail above. Changes and modifications may be made withoutdeparting from the invention. It covers all modifications within thescope of the following claims.

1-28. (canceled)
 29. A method of failure avoidance when synchronizing atransceiver end and a receiver end by means of transmitted sequencenumbers, wherein each sequence number is not necessarily errorprotected, and wherein a received sequence number considered erroneousaccording to a predetermined criterion is disregarded.
 30. The methodaccording to claim 29, further comprising: arranging sequence numbersaccording to their time of arrival; and, purging received sequencenumbers not within a prediction interval as determined from one or moreearlier received and non-purged sequence numbers and number of one ormore transmission time intervals with no data received betweenconsecutively received sequence numbers.
 31. The method according toclaim 30, wherein the transmission time intervals are weighted by themaximum number of transmission blocks of the transport format.
 32. Themethod according to claim 31, wherein an integer is added to theweighted number of transmission intervals.
 33. The method according toclaim 30, wherein a received sequence number greater than an estimatedgreatest sequence number allowed is disregarded.
 34. The methodaccording to claim 30, a received sequence number not greater than anestimated greatest sequence number allowed is not disregarded.
 35. Themethod according to claim 29, wherein the purged sequence of sequencenumbers is passed to updating of a hyper frame number.
 36. The methodaccording to claim 35, wherein the hyper frame number is updatedaccording to a basic method.
 37. The method according to claim 29,further comprising: arranging of received sequence numbers according totheir time of arrival; and, for each decision interval, sequentiallydisregarding each one of the received sequence numbers within a decisionwindow comprising consecutively received sequence numbers.
 38. Themethod according to claim 37, wherein the decision window spans aninteger number of consecutively received sequence numbers starting withthe sequence number of the decision interval.
 39. The method accordingto claim 37, wherein the decision window spans an integer number ofconsecutively received sequence numbers starting with the sequencenumber of the most recently received sequence number.
 40. The methodaccording to claim 37, wherein the decision window spans at least fourconsecutively received sequence numbers.
 41. The method according toclaim 37, wherein for each disregarded sequence number a candidate hyperframe updating is undertaken.
 42. The method according to claim 41,wherein the candidate hyper frame updating is undertaken according to abasic method.
 43. The method according to claim 41, wherein, if, for anyone disregarded sequence number within the decision window, thecandidate hyper frame number updating results in a non-increased hyperframe number, no further sequence number is disregarded and no furthercandidate HFN updating is undertaken for the decision interval.
 44. Themethod according to claim 41, wherein, if, for any one disregardedsequence number within the decision window, the candidate hyper framenumber updating results in a non-increased hyper frame number, the hyperframe number of the decision interval is set equal to the hyper framenumber of the preceding decision interval.
 45. The method according toclaim 41, wherein, if, for all of the disregarded sequence numberswithin the decision window, the candidate hyper frame number updatingresults in the same hyper frame number, this candidate hyper framenumber is decided to be the hyper frame number of the decision interval.46. The method according to claim 41, wherein, if, for all of thedisregarded sequence numbers within the decision window, the candidatehyper frame number updating results in a hyper frame number increase,the hyper frame number of the decision interval is set equal to thehyper frame number of the preceding decision interval increased by one.47. The method according to claim 36, wherein the basic method increasesa hyper frame number if, when comparing two received sequence numbers,the most recent of the two sequence numbers is less than the othersequence number.
 48. The method according to claim 47, wherein thecomparison is made modulo an integer, the integer being equal to thecycle length of transmitted sequence numbers.
 49. The method accordingto claim 29, wherein the method avoids cipher synchronization failure.50. The method according to claim 29, wherein the method allows forreduction of redundancy being added to payload.